Ring-width variation in trees at upper treeline in the high mountains of temperate latitudes is a potentially important indicator of past climatic variations, especially temperature variations. Bristlecone pines (Pinus longaeva D.K. Bailey and P. aristata Engelm.) were sampled at nine sites in western United States. Plotted annual ring-width indices are given for chronologies that range in length from 532 years in New Mexico, 1409 years in Colorado, and 1239 years in Nevada to 1501 years in eastern California. Possibilities for increasing the length of these chronologies by incorporating tree-ring data from logs and remnants are good in several of the areas, and a 5405-year upper treeline chronology has been developed in California. Tree-ring statistics show that crossdating is poorer, the climatic response is smaller, and the autocorrelation (a measure of year-to-year persistence) is greater in trees at upper treeline sites than at sites near the arid lower forest border. Climatic response functions differ in many details, but generally indicate a positive response of ring growth to warm temperatures in the previous late summer and autumn and current spring and summer. There is a negative response to warm temperatures during some winter and early spring months at several of the sites. The effect of precipitation varies greatly, but a positive response to precipitation during the previous summer or autumn, and during the current spring or summer is indicated. Variations in needle length are related to summer temperature, and may be important in explaining the high autocorrelation of upper treeline ring-width series. Ring-width departures from the long-term mean during the past 500 years were calculated from upper treeline data for 30-year subperiods. The departures are in the same direction over the whole region during many of these subperiods, indicating that climate, rather than local ecological factors, is responsible for the ring-width variations. Comparison of tree-growth fluctuations with meteorological observations at selected stations shows that a general warming trend between the periods 1901-1930 and 1931-1960 is reflected by an upward trend in tree growth. However, low rates of tree growth during an earlier warm period (1850-1869) may be due to a lag in the response of ring -width growth to climatic changes at upper treeline.

Cores of red spruce (Picea rubens Sarg.) from three upper-elevation sites in Maine, U.S.A., were X-rayed, and minimum and maximum wood densities as well as ring widths were mechanically recorded. The 200- to 300-year series of maximum densities at the three sites show remarkable inter-site similarity. Maximum density and total ring-width series from one site, Elephant Mt., were standardized. Response functions, which measure tree-growth response to climatic variables, were calculated for each of these two series. The ring-width response function explained 66% total variance, of which 34% was explained by climate. The maximum density response function explained 70% total variance, 67% of which was explained by the same climatic variables. Thus, the climate signal from maximum densities is stronger, and perhaps more season-specific, than that of ring widths.

The relationship between archaeology and tree-ring dating, or dendrochronology, is reviewed. Until the past decade, the applications of tree-ring dating to archaeological problems had not been thoroughly exploited. Now, in addition to providing the most precise dating control in the world, dendrochronology is making contributions to behavioral archaeology and to the reconstruction of past environments.

Dendrochronological research in the Mexican state of Oaxaca in 1970 proved negative due to complacent ring series. It is suggested that this is caused by a flexible growing season triggered only by the onset of the rains. Pine and fir were sampled from eleven sites. No old age trees were located and crossdating could not be accomplished.

Bristlecone pines were sampled at four sites ranging from the arid lower forest border to the upper treeline in the Snake Range of eastern Nevada. Maximum ring-width response to environmental variation is found at the upper and lower forest limits. Ring-width index series from individual trees, as well as the mean site chronologies, were compared by cross-correlation analysis and principal component analysis, combined with digital filtering to emphasize variations in different frequency ranges. Positive correlation exists between the high-frequency variations at all sites, but the longer term trends and fluctuations at the upper treeline are negatively correlated with fluctuations at the lower altitude sites. Cross-spectral analysis substantiates the results of cross-correlation analysis and indicates that the associated variations in the upper treeline and lower forest border chronologies are concentrated in certain frequency ranges that may have climatic significance. From examination of the climatic response functions, the negatively correlated low frequency variations are tentatively judged to be related to warm- season temperature fluctuations, whereas the positively correlated high frequency variations may be related to precipitation. Frequency-dependent relationships between tree-ring chronologies, or between tree-rings and climate should be considered in the analysis of large arrays of tree-ring

A brief discussion is presented on a new measuring system based on an APPLE microcomputer. Aspects of both hardware and software are considered, with emphasis on the software that provides operator interaction. The system uses diskettes for data storage and completely eliminates both paper tape and key punch cards from the measuring process.

Tree-ring series that record climatic variation have long been of interest for study of possible effects of solar variability on terrestrial phenomena. Spectral analysis, harmonic dial analysis, digital filtering, cross-correlation and principal component analysis were used separately and in combination in an attempt to detect relationships between the annual Wolf sunspot numbers and ring-width indices, primarily from western North America. The results show no evidence of significant, consistent relationships between tree-ring data and sunspot numbers.

A widely spaced grid of tree-ring chronologies most suitable for dendroclimatic analysis of western North America is selected objectively on the basis of 1) numbers in the sample, length in years, and site locations, 2) statistical characteristics of the chronologies, and 3) correlation of chronologies with those on neighboring sites. The chronology statistics are then analyzed to characterize the quality of the selected set. The procedures used in this study are recommended for future climatic analysis to assure objectivity in the selection of quality tree-ring data and to allow comparisons of the statistics for new chronologies to the established data sets.

Skeleton plotting is an established manual technique for representing the relative narrowness of tree rings in a single radius. These plots can be used as a visual aid to crossdating. This paper describes a method for deriving these plots by computer. The method uses a low-pass digital filter, running means, and standard deviations of ring-width measurements. When the manual and computer plots are compared for the same series, approximately 85% agreement is found. Examples of results are presented for specimens from sensitive, moderate, and complacent sites. FORTRAN program listings are included for two subroutines for (a) identifying small rings and (b) producing the plot.

Three computer programs that are basic to the processing and development of tree -ring chronologies are now available. They were designed to refine and replace older programs that were previously furnished by the laboratory. Program RWLIST replaces program RWLST and is used for data inspection. Programs INDEX and SUMAC replace INDXA. INDEX is used for curve fitting procedures while SUMAC does summaries of series of indices, analysis of variance and cross-correlation. The new programs represent an increase in efficiency and flexibility in use. They are written in current ANSI Fortran IV and will be readily adaptable to most computing environments.

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